CHARLES R. STEARNS, Space Science and Engineering Center, University of Wisconsin, Madison, Wisconsin 53706
In the Ross Ice Shelf region of Antarctica, the vertical static stability of the atmosphere is usually stable to the vertical displacement of an air parcel. For example, the annual mean air temperatures for Pegasus North and Minna Bluff automatic weather station (AWS) sites in the figure and given in the table are -21.4°C and -21.7°C, respectively. In the annual mean, the air moving down from the 920-meter (m) height of Minna Bluff to Pegasus North would be 8.9°C warmer than Pegasus North and statically stable to a vertical air parcel displacement. The result is that most of the time the air flow is around, not over, terrain. Stearns and Weidner (1990, 1991, 1993) present additional wind data in the area of the Pegasus Runway.
The figure presents a composite annual vector wind direction and speed for the AWS sites given in the table. The AWS sites, located to the east of Ross Island and Black and White Islands, Laurie, Ferrell, Meeley, Tiffany, and Linda, have similar vector directions out of the south-southwest. The maximum annual wind speed directions are also similar. At Tiffany AWS site, the wind velocity is lower as is the annual mean wind speed. The vector wind direction at Minna Bluff is similar to the previous sites but with a higher velocity. One would expect other sites in the area to have similar vector directions. Manning AWS site, however, clearly shows the effect of the Minna Bluff obstacle on the surface wind as the flow is deflected to the east around Minna Bluff.
The area south and west of Ross Island has a very different flow pattern. As the air moves from Tiffany AWS site toward Windless Bight where Katie AWS site is located, it is deflected by the 200 m plus barrier formed by Mount Erebus, Mount Terra Nova, Mount Terror, and Hut Point Peninsula to flow from the northeast along Hut Point Peninsula toward Black Island and Brown Peninsula. The warmer air above 200 m flows over the Hut Point Peninsula to the west based on the records from Fogle AWS site on Hut Point Peninsula. AWS sites south of Brown Peninsula also show air flowing to the west. Slotten and Stearns (1987) reported that the pressure difference between Katie AWS site and the AWS sites of Laurie, Ferrell, and Meeley increased with increasing wind speed at Katie AWS site.
The table shows that the highest wind speeds at all AWS sites are from 175° to 246°. These are wind events in which the stability changes from stable to neutral or slightly unstable allowing the strong winds coming over Minna Bluff to reach the surface at Pegasus North and South possibly influencing the operation of aircraft from Pegasus Runway. When strong winds are present at the surface, the change of wind speed with height is sufficient to introduce a possible wind shear effect on aircraft turning to a northerly course after takeoff from either Pegasus Runway or Williams Field.
This research is supported by the National Science Foundation grant OPP 94-19128.
Slotten, H.R., and C.R. Stearns. 1987. Observations of the dynamics and kinematics of the atmospheric surface layer on the Ross Ice Shelf, Antarctica. Journal of Climate and Applied Meteorology , 26, 1731-1743.
Stearns, C.R., and G. Weidner. 1990. Wind speed events and wind direction at Pegasus site during 1989. Antarctic Journal of the U.S. , 25(5), 258-262.
Stearns, C.R., and G. Weidner. 1991. Wind speed, wind direction, and air temperature at Pegasus North during 1990. Antarctic Journal of the U.S. , 26(5), 251-253.
Stearns, C.R., and G. Weidner. 1993. Snow temperature, wind speed, and wind direction around the Pegasus Runway during 1992. Antarctic Journal of the U.S. , 28(5), 291-294.